Polished samples of Chernobyl "lava" and rich variety of trapped inclusions were studied using complementary spectroscopic methods and by electron microscopy. Spectroscopic properties of the brown "lava" variety in infra-red and visible range are dominated by contribution of nearly stoichiometric (U,Zr)O2+x (x <= 0.05-0.1). At the same time, abundant inclusions of strongly hyperstoichiometric urania are detected using electron microscopy. Their morphology, internal structure (when present) and textural relationships with other included phases indicates partial oxidation of fuel from degraded bundles. Melting and/or liquefaction of hyperstoichiometric urania occur at much lower temperatures than for ideal UO2, explaining "molten" appearance of many inclusions. Fuel-cladding interaction prior to the explosion led to formation of monoclinic and tetragonal polymorphs of ZrO2 with markedly different crystalline quality; the high temperature modifications are stabilized by uranium admixture. These phases were formed on the saturation stage of the interaction. At later stages of the accident, uranium-rich zircon crystals were formed as a result of reaction of the zirconia-based pieces with molten construction materials. Dynamic conditions in the melt pool explain remarkably complex internal structure of some zircon crystals: some of them experienced several growth-dissolution-regrowth events with clear compositional differences between the "growth"-related and "secondary" generations. Partitioning of Nb and Si between droplets of former steel and the surrounding melt allowed estimation of oxygen fugacity in the pool. Strongly reducing conditions down to IW-3.6, where IW - iron-wustite buffer, were present. Implications for the accident scenario are presented.

The basic phase and chemical composition of Chernobyl "lava" sample from the sub-reactor premise #305/2 that is located right below reactor base plate, and which is regarded as the primary melt source, are reported for the first time. The main substance of the "lava" is the X-ray amorphous glass-like material (in wt.%): Na2O 1.99, K2O 3.81, MgO 2.97, CaO 7.51, MnO 0.29, FeO 0.14, Al2O3 8.96, SiO2 64.15, TiO2 0.29, ZrO2 5.13, UO2 4.57, total 99.81). It contains small (5 to 30 mu m) inclusions of technogenic analogues of natural minerals: high-uranium zircon, (Zr0.90U0.09Si1.01O4), U-bearing baddeleyite (Zr0.90U0.10O2) and Zr-bearing uraninite (U0.83Zr0.17O2). A technogenic analogue of vorlanite, (CaU6+O4), was found to be formed on the "lava" surface during storage at Khlopin Radium Institute under laboratory conditions, which shows the low chemical resistance of "lava" to environmental impact. The obtained results are highly important for assessing the consequences of the accident at the Fukushima Daiichi Nuclear Power Plant and modeling of the long-term environmental impact to the highly radioactive materials.

Crystals of ZrSiO4; ZrSiO4: Eu3+; and ZrSiO4: (Eu3++V) have been grown by the flux method. Their structural and luminescent properties have been studied demonstrating heterogeneity in cathodoluminescence (CL) for all samples. Such a heterogeneity of CL in ZrSiO4; ZrSiO4: Eu3+ is related to irregular distribution of point defects associated presumably with oxygen vacancies. Uneven distribution of vacancies as assumed led to the formation of different sites for europium ion. Moreover, in different areas of the crystal matrix the number of sites and their types vary. Activation of zircon with europium and vanadium simultaneously caused an increase of europium incorporation in comparison with zircon doped with europium only. It was found that heterogeneity of CL properties of ZrSiO4: (Eu3++V) is related to the irregular distribution of vanadium in crystal matrix. Polarization studies of CL spectra suggest that there are at least four europium sites in ZrSiO4: (Eu3++V).

The fabrication of a photovoltaic nuclear electric battery consisting of a radioactive diamond core and an InGaP photoconverter is described. An electrical circuit for a nuclear battery has been proposed. A battery core has been manufactured using a polished self-glowing diamond plate made of artificial single-crystal IIb-diamond activated with 0.008 wt. % C-14. The optimal geometric parameters of the proposed diamond plates have been determined, and a prospective photovoltaic converter was developed. The optimal design of the nuclear diamond battery, including possible increase in power yield, is discussed.

Crystals of zircon, ZrSiO4, doped with Eu and V simultaneously have been grown for the first time by the flux method. The use of both (Eu + V) has supported higher Eu3+ incorporation into zircon lattice and respective increase of luminescence intensity under UV-light (220 and 365 nm) in comparison with zircon doped with Eu3+ only. The irregular distribution of vanadium and appearance of blue color in some zones of crystal matrix have been observed and studied using optical and scanning electron microscopy, electron probe microanalysis, cathodoluminescence imaging and spectroscopy. Further research is proposed on study of valence states of vanadium in zircon lattice and possible improvement of synthesis conditions in order to avoid formation of blue color suppressing the luminescence.

Samples of crystalline cubic phased ceramics based on (Zr1-& khcy;Hf & khcy;)(0.82)Y0.17Eu0.01O1.91 with different contents of hafnium (& khcy; = 0; 0.21; 0.50; 0.77; 1) were synthesized. The synthesis conditions were chosen to avoid the possible formation of a minor tetragonal phase. The average grain size was 2-5 microns. The structural parameters of ceramics, their band gap, luminescent and thermoluminescent properties were studied depending on the hafnium content. It was shown that single-phase sample with calculated formula ((Zr0.77Hf0.23)(0.82)Y0.17Eu0.1)O-1.91 demonstrated the highest cathodoluminescent intensity upon excitation by electrons. It was found that thermoluminescent properties of ceramics with hafnium content of & khcy; = 0.50-0.77 range are prospective for application in thermodosimetry. The highest luminescence yield was observed in such samples.

For the first time a self-glowing blue-colored single crystal diamond (weighing 0.14 g) was synthesized by method of temperature gradient at high-pressure and high-temperature (TG HPHT) using starting precursor activated with carbon-14 in the form of BaCO3. The total content of 14C in the crystal matrix is estimated 0.008 wt.% or 1.8 MBq in total. The diamond emits intrinsic radioluminescence, which is visually observed in the dark. Basic properties of this diamond are discussed.

Complex oxides of Y3Al5O12, Gd(Nb,Ta)O4, (Zr,Hf,Y)O2, (Zr,Y)O2, activated with trivalent rare earth ions Nd3+, Eu3+ and Tb3+ have been studied in terms of their luminescent properties. These materials are promising scintillators with high radiation, chemical, and mechanical stability. The aim of the work was to develop ceramic radiation-resistant scintillators based on oxides activated by rare-earth ions. The study included: an evaluation of changes in the intensity and kinetics of luminescence decay from single crystal samples to ceramics; a study of the complete or partial replacement of light elements by heavier ones effect on the luminescent properties; a study of the possibility of using a sensitizer to increase the luminescence yield when luminescence is excited by an electron beam of medium energies.

Two crystalline phases, which are analogues of common secondary uranyl minerals, namely, becquerelite (Ca[(UO2)6O4 (OH)6]·8H2O) and phurcalite (Ca2[(UO2)3O2 (PO4)2]·7H2O) were identified on the surface of a Chernobyl corium-containing sample affected by hydrothermal alteration in distilled water at 150 °C for one year. Phases were characterized using Single-Crystal X-ray Diffraction Analysis (SCXRD) as well as optical and scanning electron microscopy. Features of the structural architecture of novel phases, which come from the specific chemical composition of the initial fragment of Chernobyl sample, are reported and discussed. Precise identification of these phases is important for modelling of severe nuclear accidents and their long-term consequences, including expected corium–water interaction processes at three damaged Units of the Nuclear Power Plant Fukushima Daiichi.

Detailed understanding about the chemical and physical properties of the Chernobyl "lava" and other radioactive meltdown products is of paramount importance for the support of decommissioning operations and nuclear accident modelling. In this study, we provide new results about the chemical composition and structural properties of the Chernobyl "lava" matrix obtained by electron microprobe analysis and confocal Raman spectroscopy. Based on the compositional data, a principal component analysis (PCA) was conducted to visualize compositional features of the black and brown "lava", considering data from previous studies. In addition, an inverse modelling approach was performed to assess fractional contributions of construction materials that potentially contributed to the "lava" formation process. The results of the PCA show three varieties of "lava". Different fractional contributions of UO2-fuel and Zr-cladding indicate the formation of at least two distinct sources of coium melt, respectively, for the black and brown "lava". For the brown "lava", the high concentration of Mg is explained by the melting and assimilation of 23% serpentine stemming from the lower reactor shield. The black "lava" shows a high contribution of concrete (43%). Significant differences in the Fe concentration of the black "lava", as well as macroscopic flow patterns are indicative for a progressive melt formation. However, the cooling of the "lava" occurred relatively fast, forming a metaluminous glass with local variations in the degree of polymerization. Sub-microscopic inclusions of (U1-xZrx)O2 and (Zr1-xUx)O2 solid solutions point to a fractionation of U from an highly oversaturated melt. Based on the new results, the current hypothesis about the "lava" formation process is discussed and reviewed, questioning the existence of one homogenous source of melt and its stratification into layers of black and brown "lava", before spreading and solidification of the melt.

Chemical degradation of borosilicate glass doped with 238Pu was modelled in conditions of a failed underground radwaste repository in granite host rock with bentonite buffer material after penetration of aqueous solutions at temperature of 90 °C. The total duration of the experiment exceeded two years. It is shown that wet bentonite preserved its barrier function and prevents migration of plutonium to the solution. The total amount of plutonium adsorbed on bentonite clay during the experiment did not exceed 0.02% of the initial amount of plutonium in the glass sample. Estimated accumulated dose of self-irradiation of the glass sample after the experiment varies from 3.16 × 1015 to 3.39 × 1015 α-decays per gram, which is equivalent to more than 1000 years storage of 239Pu doped sample with the same Pu content. Beishan granite remained intact, with no evidence of Pu penetration into the granite matrix along mineral grain boundaries.

In this work samples of ZrO2-Y2O3-Eu2O3 and HfO2-Y2O3-Eu2O3. ceramics are synthesized. Cathodoluminescent studies were carried out. It is shown that, under the chosen synthesis regimes, the ZrO2-Y2O3-Eu2O3 ceramic is stabilized in the cubic phase and is single-phase. The HfO2-Y2O3-Eu2O3ceramic is also stabilized in the cubic phase with small amount of inclusions of the tetragonal phase. Also, in the HfO2-Y2O3-Eu2O3 sample, an inhomogeneous distribution of point defects associated with oxygen deficiency is observed.

The purpose of this work is development of glasses for radioactive materials encapsulation. Borosilicate-based glass systems R7/T7 (B2O3-ЅіO2-Al2O3-Na2O-СaO) doped with Eu3+, with various concentrations of activator were studied. The composition of the obtained glasses was investigated using electron-probe microanalysis technique. Optical properties of glasses were investigated using the following methods – cathodoluminescence, photoluminescence and absorption spectra. The range of the optimal activator concentration was determined.Samples of borosilicate glass (B2O3-ЅіO2-Al2O3-Na2O-СaO) doped with varied content of Eu3+ were synthesized and studied using electron probe microanalysis (EPMA) and optical techniques such as cathodoluminescence (CL), photoluminescence (PL) and light absorption spectroscopy. Glass composition was related to development of nuclear waste form or encapsulation matrix with sufficient resistance to radiation damage. It was observed that electron beam irradiation suppresses intensity of glass cathodoluminescence and this process is correlated with sodium diffusion outside irradiated area at comparable interval of time

Yttrium and lutetium xenotime-structured orthophosphates doped with trivalent erbium have been synthesized in the form of single crystals using flux method in the melt of Li2MoO4-MoO3 in air. Structural parameters, coherent scattering region and average microstrain have been determined by the X-ray diffraction technique. Cathodoluminescent study has shown an inhomogeneous distribution of defects, which initiate luminescence, although electron-probe microanalysis has shown a uniform distribution of Er activator in crystal matrices. The effect of intrinsic defects on the intensity of erbium luminescence bands has been studied and discussed.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

During initial stages of severe nuclear accident at Chernobyl NPP on 26 April 1986 interaction between U-oxide fuel and Zr-cladding has occurred and a corium melt (Zr–U–O) formed in localized part(s) of reactor core. In this paper, we describe the properties of unique set of samples formed during interaction of the corium melt with steel in the core that was expelled from the reactor shaft into reactor premises and subsequently oxidized. These samples primarily consist of Fe–Cr oxides with inclusions of U- and Zr-based oxides. Uranium is heavily oxidized, forming U4O9 and U3O8. Nb/Zr ratio of the inclusions and presence of substantial Ni in the oxide matrix permitted us to identify precursor materials of the studied samples. The studied material was formed in two principal stages: interaction of liquefied fuel with Zr from walls of technological channels and/or guide rod, and subsequent reaction with steel parts located in a very well-defined part of the core – the bottom part of the guide rod and/or graphite/guide rod socket on the reactor base plate. The differences in texture between the samples are ascribed to a cooling regime and substrate on which the ejected melts were cooled. Submicron particles of fission products (Pd, Ru, Tc, etc.), very rare for Chernobyl samples, are scattered within the Fe–Cr oxide matrix. Their preservation was the result of highly oxidative conditions. Leaching of 137Cs and Am in hot aqueous fresh and saline solutions was studied. High leach rates of these nuclides is ascribed to highly oxidized state of U-containing phases. Results of the current study are compared with experiments on molten corium – vessel steel interaction and provide new details on progression of the Chernobyl NPP core destruction shortly before and during the explosion.

Samples of Chernobyl fuel debris, including massive corium and “lava” were collected inside the Chernobyl “Sarcophagus” or “Shelter” in 1990, transported to Leningrad (St. Petersburg) and stored under laboratory conditions for many years. In 2011 aged samples were visually re-examined and it was confirmed that most of them remained intact, although some evidence of self-destruction and chemical alteration were clearly observed. Selected samples of corium and “lava” were affected by static leaching at temperatures of 25, 90 and 150 °C in distilled water. A normalized Pu mass loss (NLPu) from corium samples after 140 days was noted to be 0.5 g/m2 at 25 °C and 1.1 g/m2 at 90 °C. For “lava” samples NLPu was 2.2–2.3 g/m2 at 90 °C for 140 days. The formation of secondary uranyl phases on the surface of corium and “lava” samples altered at 150 °C was confirmed. The results obtained are considered as an important basis for the simulation of fuel debris aging at Fukushima Daiichi nuclear power plant (NPP).

This work is devoted to the study of self-glowing crystals containing alpha-radionuclides based on YPO4: Eu3+,238Pu, ZrSiO4:Tb3+,238Pu and ceramics based on cubic ZrO2:Eu3+,238Pu obtained in 2006, 2011, and 2017, respectively. The decay of a radionuclide causes radioluminescence of emission centers in the crystal causing its self-glowing. The paper presents the results of theoretical calculations of the energy conversion of alpha particles formed as a result of the radioactive decay of 238Pu, investigates the effect of radioactive decay on the luminescent properties of crystals, and proposes a method for estimating the power density of luminescence excitation during alpha decay. As a result of this work, the main ways of increasing the light yield for self-glowing crystals are proposed.

The paper consists of two main parts: a microscopic and spectroscopic investigation of the single crystal of 17-year-old 238Pu-doped Eu-monazite, and a theoretical calculation of the properties of several structural types of orthophosphates. It is shown that actinide-doped monazite is prone to the formation of mechanically weak, poorly crystalline crust, presumably consisting of rhabdophane. Its formation is likely promoted by the formation of peroxides and, potentially, acidic compounds, due to the radiolysis of atmospheric moisture. The calculations of mixing the enthalpies and Gibbs energies of binary solid solutions of Pu and rare earth element (REE) phosphates that were performed for the principal structural types—monazite, xenotime, rhabdophane—show that, in the case of light REEs, the plutonium admixture is preferentially redistributed into the rhabdophane. This process strongly affects the behavior of actinides, leached from a monazite-based waste form. The applications of these results for the development of actinide waste forms are discussed. The current data on the behavior of real actinide-doped monazite suggest that this type of ceramic waste form is not very resistant, even in relatively short time periods.